1. Field of the Invention
This invention pertains to processing thin sheets, and more particularly to apparatus that accurately cuts round pieces of material from a large sheet.
2. Description of the Prior Art
It is frequently desireable to cut circular pieces from a sheet of material. A well known way to cut circular pieces is with a scissors. However, in many cases, using a scissors is not acceptable. As one drawback, an outline of the circle must first be drawn on the material. For an accurate circle, another tool, such as a compass, is required. The point of the compass invariably penetrates the material, which is highly undesireable in many situations. Further, the edge of the cut piece is only as accurate as the skill of the person can make it by simultaneously manipulating the scissors and the sheet. In addition, the compass and scissors method is laborious and time-consuming.
To overcome the problems inherent with cutting circular pieces with a scissors, circle cutting punches have been developed. The cut pieces are very accurate, and high production is obtainable. On the other hand, the dies for circle punches are expensive, and a different die is required for each size piece.
Circle cutting machines are another solution to the problem of accurately cutting circles from a sheet of material. Some prior circle cutting machines included an annular metal base with a cross-piece, a handle rotatable in the base cross-piece, a cutting arm held in the handle, and a cutting element on the cutting arm. The cutting arm was normally adjustable to enable different size circles to be cut. The base was manually held tightly over a sheet of material at the proper location such that the circle to be cut was viewable through the inside of the base. Rotating the handle while pushing it toward the sheet caused the cutting element to travel in a circle and cut the desired piece from the sheet. Neil Enterprises, Inc. of Vernon Hills, Ill., and Badge Parts, Inc. of Milwaukee, Wis., are two sources of such circle cutting machines. A few prior circle cutting machines did not not have any capability of adjusting the cutting arm; a different machine was required for each size circle to be cut.
U.S. Pat. No. 4,426,781 shows a circle cutter for making paper disks that has a very limited adjustability of the cutting arm. The cutting arm is built into an annular ring that is guided for rotation in a base. Another variation of prior circle cutting machines employs a ring that is slideable over a central plunger. The ring holds an adjustable cutting arm. The plunger is pressed against a sheet of material, and the ring is rotated to cut a circular piece. An example of the ring and plunger type circle cutting machine is disclosed in U.S. Pat. No. Des. 409,630. A somewhat similar product is marketed under the designation xe2x80x9cNT Circle Cutter C1500.xe2x80x9d Another type of typical cutting machine is marketed by Neil Enterprises, Inc. under the trademark Creativety Cutter. That particular machine is adjustable to cut circular pieces ranging in size from approximately 2 xc2xc inches to 7 xe2x85x9c inches.
Despite the variety of prior circle cutting machines presently available, none is without limitations. A major problem with the prior machines was the difficulty in accurately positioning the machine on the sheet to be cut. In many applications, it was required to accurately cut around a pattern that was pre-printed on the sheet. The prior plunger and ring machines were especially difficult to center properly over the pattern to be cut. The plunger could smudge or smear the print on delicate materials such as photographs. Machines with annular bases and cross-pieces were also difficult to position, because the patterns were invariably smaller than the base. To assist in accurately positioning the machine on the pattern, a user sometimes bonded a piece of cardboard to the bottom of the base. The cardboard had a hole through it of the same diameter as the pattern. The cardboard served as a centering template that aided in accurately cutting the pattern. However, the cardboard had to be removed and a new cardboard bonded to the base for each size circle to be cut.
In another attempt to use a centering template, a loose piece of cardboard or similar material was inserted into an annular base from the top of the machine. It proved very difficult to manipulate the template past the base cross-piece and around the handle and cutting arm in order to properly seat it on a flange in the base. After the template finally was in place, it was spaced from the underlying sheet a distance equal to the thickness of the base flange. The distance between the template and the sheet introduced parallax, which reduced the accuracy of the centering process. Maneuvering the user""s head and eyes to overcome the parallax required additional undesireable time and effort.
Another drawback of prior annular base and cutting arm machines was the difficulty in changing the cutting element when it had worn. In one prior machine, for example, the entire handle had to be disassembled from the base in order to change the cutting element. Moreover, a tool such as a screwdriver or wrench was needed for the disassembly and reassembly process. A related handicap was the difficulty in adjusting the cutting arm to the proper radius. In most cases, a trial and error procedure was required to set the proper cutting radius, and a tool was invariably needed.
In general, the prior circle cutting machines were cumbersome and time consuming to set up and operate. A need therefore exists for improvements in circle cutting machines.
In accordance with the present invention, a circle cutting machine cuts circular pieces from a sheet of material in a more efficient manner than was previously possible. This is accomplished by apparatus that includes interchangeable templates that are removeably installed from the bottom of the machine base.
The base is annular in shape, having an outer diameter, an inner diameter, and a wall. The base has a cross-beam with a center bearing that defines an axis of rotation. On the base bottom surface are a number of segments, each having an inside edge. The segments are separated from each other by circumferentially spaced gaps. The base bottom surface and the segments cooperate to define arcuate grooves having a diameter between the base inner and outer diameters.
The base center bearing receives a hollow shaft of a handle. On one end of the shaft is a crank with a hand knob. A handle spring between the crank and the base cross-beam biases the shaft to slide in an upward direction in the center bearing. On the shaft second end, on the opposite side of the base center bearing as the crank, is a cross-hole that slideingly holds a cutting arm. Upward sliding of the shaft in the center bearing is limited by contact of the cutting arm with the center bearing.
An adjuster is part of the machine handle. The adjuster includes a locking device inside the shaft that is capable of resiliently contacting the cutting arm. An adjuster knob is adjustable in the shaft to press the resilient locking device with greater or lesser force against the cutting arm. The cutting arm is free to slide in the shaft cross-hole when there is a weak force against the cutting arm. When a strong force is against the cutting arm, it is rigidly locked in place in the shaft. If desired, the cutting arm may have detents at selected locations on it.
On one end of the cutting arm is a cutting element such as a cutting wheel or a static blade. Normally, the cutting arm is inside the base wall between the cross-beam and the plane of the base bottom surface.
Another important feature of the invention is that the cutting element is very easily replaced when worn. For that purpose, the handle shaft has a relatively long length between the base center bearing and the crank. The handle is slideable in the center bearing against the handle spring a distance sufficient to locate the cutting arm completely below the plane of the base bottom surface. Consequently, the cutting arm can be removed from the shaft by loosening the adjuster knob and sliding the cutting arm out of the shaft cross-hole. In that manner, the cutting arm is removeable from the machine without the use of any tools. With the cutting arm out of the machine, the cutting element is easy to replace.
Further in accordance with the present invention, the template is made of a thin but tough and flexible material. It is formed with a circular periphery having a number of flats. The diameter of the circular periphery is slightly less than the diameter of the grooves in the base. Preferably, the number and locations of the flats correspond to the number and locations of inside edges of the segments. A tab protrudes from one of the flats.
To use the circle cutting machine, the adjuster knob is loosened. The cutting arm is slid in the handle shaft cross-hole such that the cutting element is at the desired distance from the base axis of rotation. The detents in the cutting arm aid in setting the proper location of the cutting arm within the shaft. The adjuster knob is tightened to lock the cutting arm in place.
A desired template is installed in the base. That is achieved by fitting the template flats inside the segments inside edges, and placing the template circular periphery on the base bottom surface. The template is then pivoted by means of the tab such that the junctions between the flats and the adjacent circular peripheries enter the grooves between the segments and base bottom surface. The template is pivoted until the tab is located in a gap between two segments. At that point, the template is installed, and it lies close to the base bottom surface.
If the template does not have a guide hole in it, the machine segments are placed on a hard surface. The hand knob is pushed to slide the handle in the base center bearing until the cutting element contacts the template. Then the handle is rotated while pushing on the hand knob to cut a guide hole that is the size of the pieces of material to be cut with the machine. The long handle length enables the crank to easily clear the hand of a person that holds the machine in place during operation. The machine is then laid on the sheet to be cut, and the template guide hole is centered over the pattern. The thin and flexible template material enables it to be pushed the small distance to contact the sheet and thereby eliminate any parallax. Turning the handle a few turns while pushing on the hand knob cuts a perfectly centered circular piece. At any time, the template can be removed from the machine by pivoting it to bring the circular periphery out of the segment grooves, and a new template installed.
The method and apparatus of the invention, using interchangeable templates, thus cuts exact circular pieces from a sheet of material. The probability of misaligning the machine over a pattern to be cut is remote, even though the machine can cut a large number of different circle sizes.
Other advantages, benefits, and features of the invention will become readily apparent to persons skilled in the art upon reading the detailed description of the invention in conjunction with the accompanying drawings.